It should be evident that some, but not all, subtasks are checked from higher up in the task list.
For instance, in the grocery list, it should be evident that there are a few items checked in a main category. If you check the category - fruits, all the sub-items are checked, If you only check a few sub-items, there is no way of telling from the category view that anything is checked. A semi-shaded check mark in the category would work.
Agree with Anonymous and R Nick
R Nick commented
I support the request and would like to add that the main task automatically needs to get checked when all sub-tasks have been checked. At the moment it is silly especially in the Android app where there is no tree view (MUCH NEEDED!!!) that main tasks appear to have to be done when all sub-tasks have already been completed.